[hubertus65]

Adds ImpactFailures.IfExpressionDifferentSizesInFunction, a minimal model with MSL 4.1.0 that fails in Modelon Impact (impact.modelon.cloud, checked 2026-10-31).

Failure: OCT rejects both functions:

Error at line 21, column 10, in function 'Modelica.Mechanics.MultiBody.Frames.TransformationMatrices.smallRotation':
    If-expression with branches that have different array sizes must have parameter test-expression:
    {T[2,3], - T[1,3], T[1,2], T[1,1] - 1, T[2,2] - 1, T[1,1] * T[2,2] - T[2,1] * T[1,2] - 1} has size [6]
    {T[2,3], - T[1,3], T[1,2]} has size [3]

Trigger: phi := if withResidues then {...6 elements...} else {...3 elements...},
where withResidues is a function input, not a parameter expression. This follows the
specification rule that branches of different sizes need a parameter condition, so the MSL code is the
problem here rather than OCT. OpenModelica 1.27.1 accepts it.

Workaround in the MSL: modelica#4848 assigns phi in an
if-statement. Its size is already fixed by the declaration phi[if withResidues then 6 else 3].
OpenModelica results are bit-identical, and OCT compiles and simulates the changed functions.

Upstream MSL pull request: modelica#4848

🤖 Generated with Claude Code

https://claude.ai/code/session_01UmNZkRw6HV9CeBvNk36AzT